The present invention relates to a gas-permeable element of a refractory material for blowing of gases into metal treatment vessels through their lining.
Oxygen blowing processes which serve for pig-iron refining have been improved in metallurgical sense by controlled blowing of secondary gases such as nitrogen or argon through the converter bottoms. Also, in vessels for oxygen bottom blowing processes and metal treatment, such as furnace ladles, desulfurization ladles and the like, blowing of gases into the metal bath through the vessel bottom or the lining of the vessel wall have been taken into consideration.
The gas-permeable elements which are insertable into the lining of the vessel must satisfy the requirements that their service life corresponds to the life of the remaining refractory lining, since an exchange of worm gas-permeable blocks in hot condition is difficult. Furthermore, the gas passage must be both continuous and especially also discontinuous. In other words, the vessel must be operable also without the gas passage, and after the repeated resumption of the gas supply the insertable elements must be gas-permeable in unchanged manner. Moreover, the gas-permeability of the elements over their time of use, or in other words over an entire campaign must be retained substantially identical.
The above-mentioned requirements are satisfied in the refractory gas-permeable element which is described in the U.S. Pat. No. 4,340,208. The element disclosed in this reference is provided with a metal housing arranged on its longitudinal sides, a free inner end surface, a gas-distributing chamber for a gas supply at the outer end surface, and a local opening extending in the interior of the element for a gas passage between the end surfaces and provided with a metal insert. This element can be composed of segments or strips of a refractory material and metal inserts in the form of steel sheets arranged alternatingly with one another. As disclosed in the LU 81,208, these metal inserts can be flat, wave shape, tubular or wire shaped and have a small wall thickness.
In all these gas-permeable elements the gas passage takes place through narrow gaps which remain between the refractory material and the metal inserts. The refractory material is loaded with the gas pressure which causes a plurality of disadvantages. For preventing lateral swelling of the metal housing which surrounds the refractory material and a lateral discharge of gas into the surrounding masonry which can cause a premature wear, the metal housing must be composed of a steel sheet with a relatively great wall thickness with provision of gas-tight welding seams. For preventing the undesirable and uncontrollable gas passage along the inner wall of the metal housing, a mortar layer must be arranged between the refractory material and the metal housing, which is difficult to put in. When nitrogen is used as a scavenging gas, nitrogenization and also simultaneous carbonization by the frequently carbon-containing refractory material, of the metal housing takes place. Both these processes lead to brittleness and formation of cracks which can undesirably affect the gas passage. When CO.sub.2 is used as a scavenging gas, the carbon-containing refractory material is depleted of carbon, and it must be protected at all sides by sheet layers or by lining.
Furthermore, there is a danger that the refractory material is pressed under the action of the gas pressure from the metal housing outwardly and into the metal bath, which can lead to a breakage of the metal bath through the lining.
The EP-A 64,449 discloses an arrangement for blowing of scavenging gas through the bottom or the wall of a converter for metal refining. It includes a distributing chamber which is mounted on the outer surface of the converter wall and is provided with a gas supply. A plurality of cylindrical nozzle pipes extend from the distributing chamber and pass through the converter wall, the permanent lining and the wear lining and extend to the inner surface of the lining. These nozzle pipes are flattened in the region of the wear lining by compression to the inner width of maximum 1mm and advantageously are embedded in respective recesses of the wear lining block. The mounting and replacement of such a blowing device is expensive and time consuming, and at best it can be used effectively only for small converters.